ABC notation has been around since the 70’s and is a simple way of encoding musical notation using standard text and grammatical symbols. It is easy to edit and share with others using the copy/paste function on most devices and all ABC software allows the melody to be played at any speed. It was very quickly adopted by the players of Celtic music due to it’s simplicity and ease of use. This website abcnotation.com is the easiest way to learn the basics. The main website thesession.org , used by trad players all over the world uses ABC notation and makes it easy to add tunes to your personal collection of tunes.
Here http://michaeleskin.com/abctools/abctools.html is a fantastic online ABC tool which allows you to change the key of tunes, add tab notation for mandolin (banjo and fiddle), tab for various guitar tunings, tab for bouzouki or mandola, tin whistle fingering charts and will also let you add the note names under the musical notation. Simply copy/paste the ABC notation into the page and see what it can do. The page doesn’t play the melody but if you hit the ‘play’ button it will open the notation in this page https://editor.drawthedots.com/ which will play back the melody with chordal accompaniment (if included in the ABC notation).
You will also need some software to turn the ABC notation into standard musical notation such as this online player and editor or by downloading a dedicated app such as “the Craic” available for apple devices (highly recommend).